Effect of COOH group on the performance of rhenium (I) tricarbonyl complexes with tetrathiafulvalene-fused phenanthroline ligands as dyes in DSSC: DFT/TD-DFT theoretical investigations

A series of rhenium (I) tricarbonyl complexes Re(CO)3Cl(HnL) (n = 1, a1–a3; n = 2, b1–b9; L = 4′, 5′-bis(carboxyl)dithiotetrathiafulvenyl[4,5-f] [O’regan,Nature,353:737-740, O’regan and Gratzel 1991;Drgnonetti C,Inorg Chim Acta,388:163-167, Dragnonetti et al. 2012] phenanthroline; a and b indicate the number for COOH group; 1–9 indicates different positions for COOH group on phenanthroline) have been investigated theoretically to explore the effect of COOH functional group on their electronic structures, spectroscopic properties, and their properties as dye in a solar cell. The different numbers and positions of carboxyl group on phenanthroline (Phen) ligand in designed complexes significantly changed the HOMO–LUMO energy gap smaller than the parent complex Re(CO)3Cl(L) (2). Therefore, the absorptions of most designed complexes have an obvious red shift compared with 2. Furthermore, the values of driving force (D) and light-harvesting efficiency (LHE) have been calculated and compared. According to the results above, we find 2-position COOH (a2) and 2,3-position COOH (b9) own both good optical properties and enough driving force, and predict that a2 in a1–a3 and b9 in b1–b9 may have better performance as the dye sensitizer than other designed dyes.